With the recent digitalization of terrestrial and satellite television broadcasting, it has become possible to transmit a comparatively large volume of program information together with program content. A typical example of the program information is electronic program guide information.
The technique to compress moving images, which has been obtained from the digitalization of broadcasting, has made it possible to broadcast an extremely large amount of program content. This approach, however, requires a mechanism which allows the viewer to easily choose from a large number of programs. The most typical mechanism to meet this demand is an electronic program guide. By displaying an electronic program guide on the screen of a television receiver, the viewer can choose a program without checking a TV program page in a newspaper or a TV program magazine. When the amount of the information to be displayed is too large to fit within the screen, the viewer can generally scroll the screen vertically and horizontally in the same manner as in a personal computer.
With the development of the broadband IP network, on the other hand, IP moving-image distribution service is spreading because of its bidirectional communication feature. While digital broadcasting can provide only programs which are currently being broadcast, the IP moving-image distribution service stores past broadcast programs in servers and distributes the programs upon request from individual viewers. This service, which is an example of what is called VOD (Video On Demand) service, is attractive to viewers who want to watch past broadcast programs that they missed or recommended by friends.
Similar to the case of choosing currently broadcast programs, the IP moving-image distribution service requires a mechanism which allows the viewer to easily choose a desired past program. The number of programs to be chosen by the viewer is so large that, without a simple choice function, the mechanism is not viewer-friendly.
To meet this demand, the following approach has been suggested (see, for example, Patent Literature 1). A television receiver displays on a screen two types of electronic program guide information together as a combined electronic program guide. One of the two types of the information is received via a broadcast path, and the other type is received via a communication path (generally, IP network). If the viewer chooses a currently broadcast program on the electronic program guide, the chosen program is obtained via the broadcast path and displayed. When the chosen program is a past program, it is obtained from an image distribution server via the communication path and displayed. This mechanism allows the viewer to seamlessly search the past, present, and future electronic program guides on the same screen, thereby greatly reducing the workload of the viewer in program choice.
The two types of electronic program guide information are combined by the television receiver in Patent Literature 1, but it has been suggested to combine them on the transmitter side (see, for example, Patent Literature 2). According to this mechanism, the two types of electronic program guide information are previously combined on the transmitter side to avoid complex processing on the receiver side.
Seamlessly displaying the past, present, and future electronic program guides can enhance the convenience of viewers, but the following problem remains unsolved. In the approach of Patent Literature 1, the two types of electronic program guide information received respectively via the broadcast and communication paths have to be combined by the viewer's television receiver. This makes the television receiver complex and high cost.
In the approach of Patent Literature 2, on the other hand, the electronic program guide information to be transmitted always contain a large amount of electronic program guide information from past to present. The large amount of data results in a high transmission load, regardless of whether it is received via the broadcast or communication path.
Furthermore, the approaches of Patent Literatures 1 and 2 both require the viewer to take the trouble to start and display the electronic program guide in order to watch a past program.
Citation List
Patent Literatures                Patent Literature 1: Japanese Patent Unexamined Publication No. 2004-193920        Patent Literature 2: Japanese Patent Unexamined Publication No. H11-341371        